In its 16 years of scientific measurements, the Spitzer Space Telescope performed ground-breaking and key infrared measurements of Solar System objects near and far. Targets ranged from the smallest planetesimals to the giant planets; Spitzer helped us to reshape our understanding of these objects while also laying the groundwork for future infrared space-based observations like those to be undertaken by the James Webb Space Telescope in the 2020s. In this Review Article, we describe how Spitzer advanced our knowledge of Solar System formation and evolution through observations of small outer Solar System planetesimals—that is, comets, centaurs and Kuiper belt objects (KBOs). Relics from the early formation era of our Solar System, these objects hold important information about the processes that created them.We group Spitzer’s key contributions into three broad classes: characterization of new Solar System objects (comets D/ISON 2012 S1, C/2016 R2 and 1I/‘Oumuamua); large population surveys of known objects (comets, centaurs and KBOs); and compositional studies through spectral measurements of body surfaces and emitted materials.
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We thank NASA, JPL, Caltech and the Spitzer project, without which none of the science described above would have been possible. As a NASA mission, local Solar System science measurements could have been downplayed or marginalized, but this was never the case. Instead, the authors experienced Spitzer observing schedules built around some of their time-critical observations, and large amounts of legacy science dedicated to their surveys. Project staff were welcoming and friendly but also highly professional and competent. The science return of NASA efforts like the Deep Impact, Stardust and OSIRIS-REx missions, and the ISON and ‘Oumuamua observing campaigns, were greatly enhanced by Spitzer’s observations. Notable support was provided by many, including L. Armus, S. Carey, C. Grillmair, G. Helou, R. Hurt, V. Meadows, L. Rebull, N. Silberman, G. Squires, T. Soifer, L. Storri-Lombardi and M. Werner. E.F.-V. also acknowledges support from the 2017 Preeminent Postdoctoral Program (P3) at UCF.
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